1. Field of the Invention
The invention relates to improvements in test specimen grip apparatus for testing machines and, more specifically, to improvements in grip apparatus for tensile stress testing machines. The grip apparatus disclosed is capable of holding test specimens, such as textile test specimens, that are wider than usual dog bone specimens or the like and, in addition, is provided with desirable fluid actuation, a thumb screw lock for its jaw members and an arrangement whereby grip inserts can be rapidly and easily removed and replaced.
2. Description of the Prior Art
This invention is an improvement in wedge grips for testing machines and, in particular in the grip apparatus disclosed in applicant's U.S. Pat. No. 4,662,229, issued May 5, 1987, entitled Grip Assembly, the disclosure of which is incorporated herein by reference. Disclosed in applicant's said prior patent is test specimen grip apparatus for use with universal type testing machines. The grip apparatus disclosed includes a grip housing having a connecting end adapted for securing the housing to tensile stress testing apparatus and a test specimen receiving end opposite the connecting end of the housing. A pair of passages extend through the connecting end of the housing and converge toward the housing's receiving end. A cavity in the housing is in operative communication with the pair of passages and with the receiving end of the housing and is adapted for receiving one end of a test specimen within the grip housing. A grip bar is slidable mounted in each of the converging passages and each grip bar extends above the connecting end of the housing. Moreover, each grip bar is provided with specimen grip means carried on its lower end, the grip means being opposed and being adapted to compressively engage oppose surfaces of a test specimen, whereby application of tensile stress to the test specimen increases the compressive engagement of the grip means with the test specimen.
Notwithstanding the patentable features and advantages of the foregoing grip assembly over those known in the prior art, applicant's prior grip assembly was not well suited for tensile testing textile materials, particularly as the tensile test specimen increased in width. A review of the prior patents disclosed or cited in applicant's U.S. Pat. No. 4,662,229, including U.S. Pat. Nos. 1,510,896; 2,419,711; 2,447,660; 2,537,322; 2,613,941; 2,676,381; 3,224,259 and 3,403,549, the disclosures of which are incorporated herein by reference, provided no structure by which textile test specimens of varying widths, such as up to at least twelve (12) inches or more in width, could be accommodated for tensile testing. Moreover, a review of additional patents disclosed in U.S. Pat. No. 4,662,229, including Canadian Pat. No. 446,096 and Soviet Union Pat. No. 800,797, the disclosures of which are also incorporated by reference, was similarly of no avail in providing or suggesting a suitable grip structure for tensile testing textile specimens of such widths as heretofore stated.
Accordingly, there remained a need for a grip apparatus for use with conventional tensile stress testing devices that was readily adaptable for use with test specimens of varying widths, including textile test specimens of up to at least twelve (12) inches or more in width. Moreover, the need for such grip apparatus included the further need for an apparatus which permits easy and rapid removal and replacement of test specimens, as well as easy and rapid removal and replacement of the specimen grip members without removal of the grip apparatus from the test device and without substantial disassembly of the grip apparatus.